modbison/backend/app/services/purchase.py

"""Marketplace purchase service: atomic escrow, fee split, item granting, refunds.

docs/planning/economy.md US-4 (task bc90d3f481b4).
"""

from __future__ import annotations

from datetime import datetime, timedelta, timezone
import math
from typing import Any

from sqlalchemy import select
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.marketplace import (
    CatalogItem,
    CreatorBalance,
    ListingStatus,
    MarketplaceListing,
    Purchase,
    PurchaseStatus,
)
from app.models.wallet import TransactionType
from app.services.wallet import InsufficientFundsError, WalletService


MARKETPLACE_FEE_RATE = 0.30  # 30% platform fee
DEFAULT_ESCROW_HOLD_HOURS = 72


class ListingNotFoundError(Exception):
    """Raised when the specified listing does not exist."""
    pass


class ListingNotAvailableError(Exception):
    """Raised when the listing is not in active status."""
    pass


class SelfPurchaseError(Exception):
    """Raised when a seller attempts to buy their own listing."""
    pass


class PurchaseNotFoundError(Exception):
    """Raised when the specified purchase does not exist."""
    pass


class InvalidEscrowStateError(Exception):
    """Raised when an operation cannot be performed on the current escrow state."""
    pass


class PurchaseService:
    @staticmethod
    def compute_fee_split(price: int, fee_rate: float = MARKETPLACE_FEE_RATE) -> tuple[int, int]:
        """Compute platform fee and seller net amount.

        Returns (platform_fee, seller_net).
        """
        platform_fee = math.floor(price * fee_rate)
        seller_net = price - platform_fee
        return platform_fee, seller_net

    @classmethod
    async def get_or_create_creator_balance(
        cls, db: AsyncSession, user_id: int, for_update: bool = False
    ) -> CreatorBalance:
        """Fetch or lazily create a creator balance row for user_id."""
        stmt = select(CreatorBalance).where(CreatorBalance.user_id == user_id)
        if for_update:
            stmt = stmt.with_for_update()
        result = await db.execute(stmt)
        cb = result.scalar_one_or_none()
        if cb is not None:
            return cb

        new_cb = CreatorBalance(
            user_id=user_id,
            available=0,
            pending=0,
            lifetime_earned=0,
        )
        db.add(new_cb)
        await db.flush()
        return new_cb

    @classmethod
    async def purchase_listing(
        cls,
        db: AsyncSession,
        buyer_id: int,
        listing_id: int,
        idempotency_key: str | None = None,
        escrow_hours: int = DEFAULT_ESCROW_HOLD_HOURS,
    ) -> tuple[Purchase, CatalogItem]:
        """Perform atomic purchase of a marketplace listing.

        Debits buyer, holds escrow, grants item to buyer, records purchase,
        and updates creator pending balance.
        """
        # 1. Lock and validate listing
        stmt_listing = (
            select(MarketplaceListing)
            .where(MarketplaceListing.id == listing_id)
            .with_for_update()
        )
        res_listing = await db.execute(stmt_listing)
        listing = res_listing.scalar_one_or_none()
        if listing is None:
            raise ListingNotFoundError(f"Listing {listing_id} not found")

        if listing.status != ListingStatus.active:
            raise ListingNotAvailableError(f"Listing {listing_id} is not active ({listing.status.value})")

        if listing.seller_id == buyer_id:
            raise SelfPurchaseError("Cannot purchase your own listing")

        # 2. Fetch catalog item
        catalog_item = await db.get(CatalogItem, listing.catalog_item_id)
        if catalog_item is None:
            raise ListingNotFoundError("Catalog item referenced by listing does not exist")

        # 3. Calculate fee split
        price = listing.price
        platform_fee, seller_net = cls.compute_fee_split(price)

        # 4. Debit buyer wallet atomically (commit=False)
        tx_idemp = f"mkt-purchase-{idempotency_key}" if idempotency_key else None
        await WalletService.debit(
            db=db,
            user_id=buyer_id,
            amount=price,
            tx_type=TransactionType.marketplace_purchase,
            reference_type="marketplace_listing",
            reference_id=str(listing.id),
            idempotency_key=tx_idemp,
            commit=False,
        )

        # 5. Grant catalog item to buyer
        granted_item = CatalogItem(
            owner_id=buyer_id,
            asset_id=catalog_item.asset_id,
            item_type=catalog_item.item_type,
            name=catalog_item.name,
            description=catalog_item.description,
            metadata_json=catalog_item.metadata_json,
        )
        db.add(granted_item)

        # 6. Mark listing as sold
        now = datetime.now(timezone.utc)
        listing.status = ListingStatus.sold
        listing.updated_at = now

        # 7. Create purchase record
        hold_until = now + timedelta(hours=escrow_hours)
        purchase = Purchase(
            listing_id=listing.id,
            buyer_id=buyer_id,
            seller_id=listing.seller_id,
            price=price,
            platform_fee=platform_fee,
            seller_net=seller_net,
            status=PurchaseStatus.pending_escrow,
            escrow_hold_until=hold_until,
        )
        db.add(purchase)

        # 8. Update seller's CreatorBalance (pending escrow)
        creator_balance = await cls.get_or_create_creator_balance(
            db, listing.seller_id, for_update=True
        )
        creator_balance.pending += seller_net
        creator_balance.updated_at = now

        # Commit everything atomically
        await db.commit()
        await db.refresh(purchase)
        await db.refresh(granted_item)

        return purchase, granted_item

    @classmethod
    async def release_escrow(cls, db: AsyncSession, purchase_id: int) -> Purchase:
        """Release funds from escrow to seller's available creator balance."""
        stmt = select(Purchase).where(Purchase.id == purchase_id).with_for_update()
        res = await db.execute(stmt)
        purchase = res.scalar_one_or_none()
        if purchase is None:
            raise PurchaseNotFoundError(f"Purchase {purchase_id} not found")

        if purchase.status != PurchaseStatus.pending_escrow:
            raise InvalidEscrowStateError(
                f"Cannot release escrow in status {purchase.status.value}"
            )

        cb = await cls.get_or_create_creator_balance(db, purchase.seller_id, for_update=True)
        cb.pending = max(0, cb.pending - purchase.seller_net)
        cb.available += purchase.seller_net
        cb.lifetime_earned += purchase.seller_net
        cb.updated_at = datetime.now(timezone.utc)

        purchase.status = PurchaseStatus.completed
        await db.commit()
        await db.refresh(purchase)
        return purchase

    @classmethod
    async def refund_purchase(
        cls, db: AsyncSession, purchase_id: int, reason: str | None = None
    ) -> Purchase:
        """Refund a purchase during the escrow hold window."""
        stmt = select(Purchase).where(Purchase.id == purchase_id).with_for_update()
        res = await db.execute(stmt)
        purchase = res.scalar_one_or_none()
        if purchase is None:
            raise PurchaseNotFoundError(f"Purchase {purchase_id} not found")

        if purchase.status != PurchaseStatus.pending_escrow:
            raise InvalidEscrowStateError(
                f"Cannot refund purchase in status {purchase.status.value}"
            )

        # Reverse seller's pending creator balance
        cb = await cls.get_or_create_creator_balance(db, purchase.seller_id, for_update=True)
        cb.pending = max(0, cb.pending - purchase.seller_net)
        cb.updated_at = datetime.now(timezone.utc)

        # Credit buyer wallet
        await WalletService.credit(
            db=db,
            user_id=purchase.buyer_id,
            amount=purchase.price,
            tx_type=TransactionType.refund,
            reference_type="purchase_refund",
            reference_id=str(purchase.id),
            metadata={"reason": reason} if reason else None,
            commit=False,
        )

        purchase.status = PurchaseStatus.refunded
        await db.commit()
        await db.refresh(purchase)
        return purchase


purchase_service = PurchaseService()